If user pictures are enabled and I edit my account, this is what is saved into the 'data' column of my users's db record:a:4:{s:7:"contact";i:0;s:5:"block";a:0:{}s:14:"picture_delete";i:1;s:14:"picture_upload";s:0:"";}

The picture_delete and picture_upload do not need to be saved and for a site with a lot of users, that's a tiny less amount of processing for unserialize in user_load().